This invention concerns industrial filters used primarily in metalworking plants to filter machining coolants to remove chips, grinding and tool wear detritus, etc., so that the coolant can be reused.
These solids to be removed include large volumes of machined chips of relatively large size, and a smaller volume of much finer particles. Vacuum filters are widely used to filter such liquids, and involve the use of woven belts overlying a perforated top vacuum box disposed at the bottom of an open tank which receives the coolant to be filtered.
Disposable sheet paper media is sometimes used to improve filter performance overlying the belt, which collects the solids and is periodically indexed out for disposal. Disposal of the paper media creates a maintenance labor burden as well as an environmental burden.
The vacuum box draws the coolant through the porous belt and/or disposable media to be filtered. The filter belt is typically overlain with a drag conveyor which is periodically advanced to move accumulations of chips on top of the belt out of the tank. The belt itself is periodically indexed with the conveyor so as to be able to be washed to clean off the filtrate. The more frequent the filter belt is indexed, the shorter its service life, and the index cycle itself interrupts filter operation reducing its capacity. Some build-up of filtered solids is desirable as this improves the clarity of the filtered liquid, as the filter xe2x80x9ccakexe2x80x9d acts as an additional filtering media. Frequent indexing reduces this beneficial effect as the solids accumulation is reduced. The machining chips rapidly accumulate in large volumes if left in the coolant when filtered, which necessitates frequent indexing. The presence of sharp metal chips on the belt also may cause the drag conveyor to tear holes in the belt by pulling the sharp metal chips along the belt surface.
It has therefore previously been recognized that it is advantageous to remove the machining chips prior to filtration to remove the fine solid particles from the used coolant.
When iron and steel chips are involved, settling tanks ahead of the filter have been used effectively, as these chips are heavy and settle out rapidly. Magnetic separators have also been used to remove iron and steel chips prior to filtration by vacuum filters.
However, in the auto and other industries, machining of aluminum has become much more widespread. Aluminum chips, being much lighter, do not settle out as well such that this approach is not effective. Magnetic separators likewise do not work with aluminum chips.
For these applications, passing the liquid through a wedgewire or perforated plate strainer has been employed to remove the chips prior to filtration in a main filter. Wedgewire is made by welding triangular in section strands of wire in parallel spaced apart arrays onto transversely extending bars to provide a slotted strainer plate. The used coolant containing the chips is directed into a smaller tank which has a wedgewire bottom plate mounted within in the upper part of the vacuum filter tank. The liquid passes out of the smaller tank through the wedgewire bottom plate and passes into the main filter tank, leaving most of the chips behind. A drag conveyor is continuously moved along the wedgewire bottom plate to carry away the chips accumulating above the wedgewire plate.
While this arrangement does remove most aluminum chips, if the wedgewire strand spacing too close, some of these chips tend to be jammed into the spaces, this tendency exacerbated by the action of the drag conveyor flights which tend to push the chips into the spaces and to deform the exposed ends over, making it difficult to clear these chips from between the wedgewire strands.
Over time, the wedgewire becomes clogged, and this necessitates periodic extended shutdowns to access the wedgewire bottom plate for cleaning. It is a difficult and time consuming process to remove the accumulated jammed chips.
For this reason, the wedgewire spacing has been increased in an attempt to minimize the tendency for clogging the same with the chips, but in this situation, many chips pass through to the filter belt, increasing the rate at which indexing must be done. If indexing is done more frequently, this reduces the average accumulation of fine solids on the belt, and this in turn decreases the clarity of the filtered coolant.
It is the object of the present invention to provide an arrangement for removing machining chips from used coolant prior to filtering the coolant in a vacuum filter, which arrangement effectively removes a very high proportion of the chips from the coolant, which arrangement is effective for removing aluminum chips, and which does not entail a substantial maintenance burden.
The above object and others which will be understood upon a reading of the following specification and claims are achieved by providing a recirculating coarse weave permanent filter belt which runs over the top of a strainer plate forming the bottom of an auxiliary tank suspended in the upper region of a main filter tank. The wedgewire strand spacing is wide enough to minimize any tendency to capture the machining chips. The permanent filter belt is returned around the bottom of the auxiliary tank. The filter belt weave is open enough to allow the suspended solids to freely pass through with the used coolant while capturing a great proportion of the metal chips. The filter belt is frictionally driven by engagement with a continuously driven drag flight conveyor which runs along the upper surface of the belt, and returns back over the top of the auxiliary tank in being recirculated, so as to diverge from the filter belt when both are being returned. The belt is preferably a coarse twill weave with the xe2x80x9cone overxe2x80x9d side engaged by the conveyor flights to establish a nonslipping positive engagement with the belt so that any tendency to drive the chips into the belt is avoided. The secure engagement between the conveyor flights and the filter belt allows the belt to be reliably driven without slippage despite being pressed onto the wedgewire tank bottom by the weight of the coolant liquid and chips bearing on it. The divergent return paths of the flight conveyor and filter belt insure that different belt areas contact the flights when engagement occurs to distribute the belt wear resulting from engagement with the conveyor flights, which, together with the nonslip engagement therebetween, greatly increases the filter belt service life.
A sloping shed plate is interposed below the wedgewire plate and the return section of the filter belt to allow the liquid passing through the filter belt and wedgewire plate to be directed to either side of the permanent filter belt and into the main filter tank.
A variable speed drive from the flight conveyor enables a manual or automatic variance in conveyor speed to accommodate changes in the chip load.
The fine solids passed through the chip removing arrangement are thus allowed to build up on the primary filter belt to improve the clarity of the filtered liquid, as the primary filter does not need to be indexed nearly as often as with the prior arrangements due to the great reduction in chip volume that must be handled by the main filter, which result increases the service life of the main filter permanent filter belt.